Communication cables are generally used to transmit a variety of signals, including voice, video, and data signals. Each cable typically contains a single or multiple strands of a transmission media (e.g., conductor often made of copper or a fiber often made of glass). In one cable design, the strands of insulated transmission media are contained within a hollow core of a tubular jacket. The insulating material, often called the insulation, confines the signals to the transmission media during transmission. While the jacket can be electrically insulating, its main purpose is to provide mechanical and environmental protection.
In addition to exhibiting many other characteristics, it is often necessary that communication cables exhibit fire resistance. When installed in buildings, communication cables are often routed through the ductwork of the building's air exchange system. Such cables are called plenum cables. One type of plenum cable often used in voice and data communication systems of commercial buildings is an UTP (unshielded twisted pair) cable. Generally, UTP types of cable contain four individually twisted wire pairs comprised of 24 AWG copper conductors. Each wire is individually insulated with an insulation material.
The insulation for the conductors in each twisted pair is typically made of one solid color for a first conductor and the second conductor contains a white color that is bandmarked or striped with the same color as the first color. Using this scheme, the conductors can always be identified as a pair even after they have been untwisted (and even when the remaining pairs in the cable become untwisted). These coloring schemes, and other identification schemes, are described in U.S. Pat. Nos. 6,293,081, 6,211,117, 6,532,329, and 6,479,607, the disclosures of which are incorporated herein by reference.
Unfortunately, none of these conventional coloring schemes for identification is completely satisfactory. Bandmarking can require the use of hazardous solvents such as methyl ethyl ketone, alcohol or cyclohexane. As well, bandmarks can cause imperfections in the insulation material and can also interfere with the product line diameter and control system, thereby causing the bandmarked conductors to be smaller than the non-bandmarked conductors. Further, both bandmarking and striping processes require additional production equipment, a bandmarking machine and a tandem extruder respectively. Finally, both stripes and bandmarks can cause a discontinuity in the insulation that can degrade the transmission integrity.